Thermal transfer systems have been developed to obtain prints from pictures that have been generated electronically, for example, from a color video camera or digital camera. An electronic picture can be subjected to color separation by color filters. The respective color-separated images can be converted into electrical signals. These signals can be operated on to produce cyan, magenta, and yellow electrical signals. These signals can be transmitted to a thermal printer. To obtain a print, a black, cyan, magenta, or yellow dye-donor layer, for example, can be placed face-to-face with a dye image-receiving layer of a receiver element to form a print assembly that can be inserted between a thermal print head and a platen roller. A thermal print head can be used to apply heat from the back of the dye-donor sheet, or to generate heat by means of radiation, such as with a laser. The process can be repeated as needed to print all colors. A color hard copy corresponding to the original picture can be obtained. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 to Brownstein.
The dye donor layer of a thermal dye donor element can be prepared by standard coating or printing techniques, for example, gravure process, spin-coating, solvent-coating, extrusion coating, or other methods known to practitioners in the art. Other methods of forming the dye donor layer can include vacuum deposition as disclosed, for example, in U.S. Pat. Nos. 5,139,598 and 5,236,739, both to Chou et al.
Classic dye donor layer coating or printing techniques typically require the use of one or more of solvents, plasticizers, binders, or other additives to provide various characteristics, such as desired viscosity, adhesion, or crystallinity. This increases the cost and complexity of the dye donor layer.